Hyponitrous acid and hyponitrites

Hyponitrous acid crystallizes from ether solutions as colourless crystals which readily decompose 

H2N2O2 Hyponitrous acid Weak acid HON=NOH, isomeric with nitramide, H2N-N02 salts are known (p. 460) 

H2N2O3 Hyponitric acid Known in solution and as salts, e.g. Angeli s salt Na2[0N=N02] 

H4N2O4 Nitroxylic (hydronitrous) acid Explosive sodium salt known Na4[02NN02]  

HNO2 Nitrous acid Unstable weak acid, HONO (p. 461) stable salts (nitrites) are known 

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HYPONITROUS ACID AND HYPONITRITES. Hyponitrous acid H N 0 is a while solid, explosive even at as low a temperature as CFC. soluble in water, more soluble in ether, can thus be extracied from water solution bv ether and the latter evaporated, water solution decomposes quickly into nitrous oxide plus water, Hyponitrous acid is nonreactive with hydriodic avid fa strong reducing agent), but reactive with permanganic acid (a strong oxidizing agent) to form nitrous or nitric acid. 

Hyponitrous Acid and the Hyponitrites. Hyponitrous acid, HgNoOo, is formed in small quantity by reaction of nitrous acid and hydroxylamine ... 

There is also considerable current environmental interest in hyponitrite oxidation because it is implicated in the oxidation of ammonia to nitrite, an important step in the nitrogen cycle (p. 410). Specifically, it seems likely that the oxidation proceeds from ammonia through hydroxylamine and hyponitrous acid to nitrite (or N2O). 

The hyponitrites (16), esters of hyponitrous acid (HO N=N OH), are low temperature sources of alkoxy or acyloxy radicals. A detailed study of the effect of substituents on k4 for the hyponitrite esters has been reported by Quinga and Mendenhall,114... 

The preparation ol the hyponitrites.—M. L. Nichols and I. A. Derbigny postulated that nitrous oxide in soln. forms hyponitrous acid N20-)-H20=(HN0)2. The several reactions in which hyponitrites are formed can be grouped as follow ... 

According to A. Hantzsch and L. Kaufmann,1 if dry ammonia be passed into the ethereal soln. of hyponitrous acid, ammonium hydrohyponitrite, (NH4)HN202, or NH4O.N N.OH, is formed in colourless crystals which melt with turbulent decomposition at 64°-65°. The salt spontaneously decomposes into ammonia, nitrous oxide, and water. The salt dissolves in water with an alkaline reaction. Ammonium hyponitrite, NH4O.N H.ONH4, cannot be prepared directly, but... 

Spectroscopic data indicate that hyponitrous acid, HON=NOH, has the planar trans configuration. Its structural isomer nitramide, H2N-NO2, is a weak acid. The structure of nitramide is shown in Fig. 15.2.2(a) in this molecule, the angle between the NNO2 plane and the H2N plane is 52°. Both trans and cis forms of the hyponitrite ion, (ONNO)2-, are known. The trans isomer, as illustrated in Fig. 15.2.3(a), is the stable form with considerable n bonding over the molecular skeleton in the cis isomer, the N=N and N-O bond lengths are 120 and 140 pm, respectively. 

This reaction is not reversible, and dissolving of N2O in water does not give hyponitrous acid. As a dibasic acid, trans-hyponitrous acid forms two types of salts acidic hyponitrites M+ HN202 that decompose readily and are more stable, and neutral hyponitrites M2+N202. Both types of salts react basic, are reductants, and are remarkably stable against reduction. 

Hyponitrous acid. In contrast to nitrous and nitric acids, hyponitrous acid crystallizes from ether as colourless crystals which easily decompose, explosively if heated. The detailed molecular structure of this acid has not been determined, but it is known that the molecular weights of the free acid and its esters correspond to the double formula, H2N2O2, that it is decomposed by sulphuric acid to N2O, and that it can be reduced to hydrazine, H2N-NH2. Infrared and Raman studies show conclusively that the hyponitrite ion has the trans configuration (a), but the N-N frequency suggests that the central bond has an order of rather less than two. ... 

Hyponitrous acid—H3N4O3—31—Known only in combination. Silver hyponitrite is formed by reduction of sodium nitrate by nascent H and decomposition with silver nitrate. 

In 2009, our research interest in the interaction of NO, molecules with metaUoporphyrins was extended to investigating the role of the heme active site independent of the nonheme site in the mechanism of action of the NORs. To this end, we sought to prepare and isolate the hyponitrite-bridged porphyrin complex [(0EP)Fe]2(A<-N202). The [(0EP)Fe]2(//-N202) complex was successfully prepared by treating a toluene solution of (OEP)Fe-(OMe) or the oxo-dimer complex [(0EP)Fe]2( -0) with hyponitrous acid (Equations 10 and 11) which may be viewed as a category 3 hyponitrite complex synthesis. See Section 3.4.1. 

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